In the case of p-hydroxyaniline mustard (having the below-given formula IV) or 5-fluorouridine (having the below-given formula V), which are known to respectively have anticancer (antitumor) action, in order to mitigate the side effects of these compounds, the following method is attempted: their hydroxyl group is temporarily esterified, no render it inactive, so that when each of these compounds is administered into an organism, the compound is converted into the active form only in cancer cells by hydrolysis with esterases in the cancer cells (T. J. Bardos et al., Ann. N.Y. Acad. Sci., 163, 1006 (1969), and JP-A ("JP-A" means unexamined published Japanese patent application ) No. 91998/1982). ##STR2##
However, the ester compounds conventionally used cannot avoid the problem that most of the compound's acyl groups are hydrolyzed by the action of esterases existing in blood before the compounds reach cancer tissue.